1. Field of the Invention:
This invention relates to circuits used to transform digitized signals. More particularly, this invention relates to hardware lookup tables used to transform digitized signals.
2. Related Applications:
The present application is related to the following U.S. patent applications Ser. No. 07/846,675, filed on Mar. 5, 1992, entitled Automatic Determination of Processing Parameters for Digitized Signal Correctors in a Digital Image Processing System to Achieve Specified Output Results; U.S. Pat. No. 5,210,711, issued May 11, entitled A Very Fast Variable Input Multibit Adder; Ser. No. 07/854,367, filed on Mar. 19, 1992, entitled Hardware Implementation of an HDTV Color Corrector.
3. Art Background:
A common method of transforming a digitized signal is to employ a hardware lookup table. A hardware lookup table is a digital memory that is pre-loaded with the appropriate transform data to perform the desired transformation. The lookup table stores transform function values for the range of input digitized signal values. The transform data is stored in the lookup table such that f(x) is stored at address x, where f is the desired function and x is the input signal. After the lookup table has been loaded with the appropriate transform data, the input digitized signal, x, is coupled to the address input of the lookup table, and the data output of the lookup table provides the transformed digitized signal f(x).
Past lookup table designs for transforming digitized signals have several limitations. Past designs using random access memory (RAM) lookup tables are not well-suited to changing the transfer function of the lookup table in real time. This is particularly true for large RAM lookup tables, since the larger the RAM, the more time required to load data into the RAM. Also, loading RAM lookup tables with functions having variable bit width required that a central processor track the lookup table address during data loading. The extra time required to maintain the lookup table address during loading made switching of transfer functions time consuming.
As will be described, the present invention provides a flexible computer controlled non-linear transform generator that employs a lookup table (LUT) having programmable controlled address and data paths. The LUT is dynamically configured into one or more banks for storing data for one or more functions, wherein the transform function is changed in real time by switching LUT banks under program control. Moreover, an auto increment load feature used in conjunction with the programmable address and data paths speeds transform data loading.